ASE L2 Exam Questions

Page 4 of 15

61.

Technician A states that diesel fuel heaters help prevent power loss and stalling in cold weather. Technician B states that diesel fuel heaters are found in a fuel line between the tank and the primary filter.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

Diesel fuel heaters help prevent power loss and stalling in cold weather, so technician A is correct. The heater is placed in the fuel line between the tank and the primary filter, making technician B also correct.

Some fuel heaters have a thermostat control that allows the fuel to bypass the heater if it has reached normal operating temperature.

62.

At what temperature will DPF regeneration be terminated?

  • 1100 °F

  • 850 °F

  • 1000 °F

  • 1500 °F

Correct answer: 1100 °F

Temperatures above 1100 °F (593 °C) will damage the particulate filter. Therefore, the regeneration will be terminated.

With the composite vehicle, the high exhaust system temperature (HEST) lamp comes on whenever the exhaust outlet temperature reaches 850 °F (454 °C) or if active regeneration occurs. The lamp flashes during parked regeneration.

63.

Using the composite vehicle on the ASE website, answer the following question:

The DEF heater relay is commanded by the ECM at ambient temperatures below what temperature?

  • 50 °F

  • 40 °F

  • 32 °F

  • 45 °F

Correct answer: 50 °F

The ECM requests heater activation when the ambient temperature is less than 50 °F. The heater relay is energized by the ECM. It provides battery voltage to the DEF system heaters to increase temperature. Coil resistance measures 90 ± 4 Ω.

64.

Using the composite vehicle on the ASE website, answer the following question:

Technician A states that the A/C high pressure switch is wired to the BCM. Technician B states that there should be a 5-V reference at pin 853.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

The A/C high pressure switch is wired to the BCM. After the switch opens at a predetermined pressure, the BCM signals the ECM to operate the cooling fans.

Based on the composite vehicle on the ASE website, the A/C high pressure switch can be tested for 5-V reference at pin 853.

65.

Using the composite vehicle on the ASE website, answer the following question:

Technician A states that four terminals are used at the J1939 public data link connector. Technician B states that there are nine terminals at the J1939 public data link connector.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

The J1939 data link connector (in-cab) has nine terminals (A-H, J). Four of these terminals are used. A is grounded at G51, while B connects to Fuse 51. C connects to pin 581 and D is connected to pin 582 at the ECM.

66.

Using the composite vehicle on the ASE website, answer the following question:

Technician A states that a regeneration is based on engine operating conditions. Technician B states that a regeneration is based on the driver's response requirement.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

A regeneration is based on engine operating conditions, DPF restriction level, and the driver's response requirement. Engine DTCs can prevent regeneration from starting or abort current regeneration.

DPF soot load determines what type of regeneration is needed. For active regeneration, vehicle speed must remain higher than 25 MPH.

67.

Using the composite vehicle on the ASE website, answer the following question:

Technician A states that if terminal 631 of the ECM was shorted to ground, the intake heater would not work. Technician B states that if terminal 621 of the ECM was shorted to ground, the intake heater would not shut off.

Who is correct?

  • Neither A nor B

  • Technician A

  • Both A and B

  • Technician B

Correct answer: Neither A nor B

Terminal 631 is the low reference ground that controls the intake grid heater relay. If the terminal was shorted, it would continuously cause the relay to remain closed, forcing the intake grid heater to constantly run.

If a short occurs at terminal 621, it causes the DEF supply pump relay to remain closed, therefore keeping the DEF supply pump running. It won't affect the intake grid heater.

68.

Technician A states that unit injectors do not require an injection pump or distributor. Technician B states that unit injectors are commonly used on advanced fuel systems.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

Unit injectors are commonly used on today's engines with advanced fuel systems, so technician B is correct. Unit injectors do not require an injection pump or distributor, which also makes technician A correct.

Diesel fuel engines use one of two setups: either nozzle fuel injectors which are used with a fuel injection pump or fuel distributor, or unit injectors.

69.

Using the composite vehicle on the ASE website, answer the following question:

What is the normal fuel pressure at test port A with the key on and the engine off?

  • 15 PSI

  • 20 PSI

  • 25 PSI

  • 30 PSI

Correct answer: 15 PSI

The electric fuel primer pump fuel pressure is 15 PSI at test port A with the key on and the engine off. With the key on and engine cranking, the low pressure supply fuel pump provides 40 PSI at test port B.

Fuel supply pressure at rated engine RPM of 1800 is between 125 and 160 PSI at test port B.

70.

Technician A states that incorrect antifreeze concentration can cause false temperature sensor readings in the ECM. Technician B states that a faulty coolant temperature sensor can cause erratic readings.

Who is correct?

  • Both A and B

  • Technician A

  • Technician B

  • Neither A nor B

Correct answer: Both A and B

Incorrect antifreeze concentration may cause the coolant temperature sensor to send faulty data to the ECM. A faulty coolant temperature sensor can also lead to erratic readings.

Faulty wiring and a faulty module can all cause incorrect readings with the scan tool. Sensors and circuits should be checked prior to condemning a module.

71.

Using the composite vehicle on the ASE website, answer the following question:

What should the voltage be on APP 1 sensor with 50% throttle?

  • 3.00 volts

  • 4.50 volts

  • 1.50 volts

  • 2.00 volts

Correct answer: 3.00 volts

The APP 1 sensor voltage varies between 1.50 and 4.50 volts with the accelerator pedal position ranging between 0% and 100%. At 50% throttle, the APP 1 sensor reads 3.00 volts, while the APP 2 sensor reads 2.00 volts.

72.

Using the composite vehicle on the ASE website, answer the following question:

What module is the ambient air temperature sensor connected to?

  • BCM

  • ECM

  • TCM

  • ICM

Correct answer: BCM

The ambient air temperature sensor is connected to the BCM. This signal is sent from the BCM to the ECM. This sensor monitors air temperature to make adjustments and is mounted on the cab.

73.

A customer describes the HPCR fuel system has trouble starting when warm, but starts okay when cold. There are no other concerns. Technician A states that a restricted air filter may be the problem. Technician B states that the injectors may be faulty.

Who is correct?

  • Technician B

  • Technician A

  • Both A and B

  • Neither A nor B

Correct answer: Technician B

Technician B is correct because HPCR injectors leak internally when they wear. The symptoms occurring with this condition include a hard hot start, but no trouble when cold.

Technician A is incorrect because a restricted air filter will lead to low power, but wouldn't exhibit a hot restart problem without other symptoms.

74.

Technician A states that a stall speed test will be high if the low power complaint is engine-related. Technician B states that a low stall speed indicates a slipping transmission.

Who is correct?

  • Neither A nor B

  • Technician A

  • Technician B

  • Both A and B

Correct answer: Neither A nor B

When diagnosing a low power condition using a stall test, a low stall speed is engine-related. High stall speed means a slipping transmission.

Normal stall speeds with low engine power can indicate other driveline problems, such as a broken engine mount. Where a stall test isn't allowed, technicians must rely on a road test or dynamometer.

75.

Technician A states that the purpose of a regeneration is to lower NOx. Technician B states that the regeneration's main purpose is to remove soot.

Who is correct?

  • Technician B

  • Technician A

  • Both A and B

  • Neither A nor B

Correct answer: Technician  B

The regeneration's main purpose is to clean soot, preventing the exhaust from becoming clogged. The DOC reduces emissions, not the regeneration process.

It is imperative for soot to be removed because it can be trapped in the lungs when breathed in, causing health issues. Soot created by diesel combustion typically measures 2.5 microns or smaller.

76.

Technician A states that a DPF must be changed periodically due to soot accumulation. Technician B states that a DPF must be cleaned periodically due to soot accumulation.

Who is correct?

  • Technician B

  • Technician A

  • Both A and B

  • Neither A nor B

Correct answer: Technician B

DPFs need to be cleaned, not replaced. This process is described as regeneration.

If the DPF reaches FULL value, it needs to be disassembled and cleaned through a special process.

77.

Using the composite vehicle on the ASE website, answer the following question:

Technician A states that during a regeneration, exhaust temperatures should be greater than 700 °F. Technician B states that during a regeneration, temperatures should not exceed 1100 °F.

Who is correct?

  • Technician B

  • Technician A

  • Both A and B

  • Neither A nor B

Correct answer : Technician B

During a regeneration, the exhaust temperatures should never exceed 1100 °F.

The high exhaust system temperature (HEST) lamp comes on whenever the exhaust outlet temperature exceeds 850 °F, or if active regeneration occurs. During parked regeneration, this light flashes. For active regeneration, the DOC must be at least 550 °F (288 °C) to react with the fuel and heat the DPF.

78.

Using the composite vehicle on the ASE website, answer the following question:

Which of the following pins are used to communicate with the scan tool on the private BUS?

  • Pins A and B

  • Pins A and C

  • Pins B and C

  • Pins C and D

Correct answer: Pins A and B

The J1939 data link connector (engine compartment) on the private network contains three pins. Pins A and B are responsible for communicating with the scan tool.

Pins C and D are responsible for communication on the J1939 data link connector (in-cab) on the public network.

79.

Using the composite vehicle on the ASE website, answer the following question:

How many levels of protection are there in the engine protection system?

  • Three

  • Two

  • One

  • Four

Correct answer: Three

There are three levels of protection: warning, derate, and shutdown. The engine protection system is responsible for monitoring the following to determine if there are any abnormal readings:

  • Coolant level
  • Coolant temperature
  • Diesel particulate filter (DPF) restriction
  • EGR exhaust gas temperature
  • Fuel temperature
  • Intake manifold temperature
  • Oil pressure
  • Oil temperature

Depending on the fault, the warning mode activates and turns on the amber CEL or MIL to alert the operator. Derate or limp mode reduces engine power 30 seconds after the first warning. Shutdown mode prevents the engine from running, so no further damage can occur.

80.

Using the composite vehicle on the ASE website, answer the following question:

How many wires does the water-in-fuel sensor have?

  • Two 

  • Three

  • Four

  • One

Correct answer: Two

The water-in-fuel sensor has two wires. When the ECM detects 130 k ohms across, it illuminates the water-in-fuel lamp.

The water-in-fuel sensor is mounted in the bottom of the primary fuel filter/water separator.